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Electronic Structure Engineering of Graphene by Strain: First-principles Calculations

Author: GuiGui
Tutor: ZhongJianXin
School: Xiangtan University
Course: Microelectronics and Solid State Electronics
Keywords: graphene first-principle strain electronic structure poisson ratio
CLC: O641.1
Type: Master's thesis
Year: 2008
Downloads: 215
Quote: 2
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Abstract


Electronic structures of graphene with different planar strain distributions have been studied using the tight-binding calculations and the first principles methods based on the density functional theory. Three types of typical strain distributions have been considered, namely, symmetrical strain distributions, uniaxial strain distributions along zigzag (ZZ) axes, and uniaxial strain distributions along armchair (AC) axes. The main results are as follows:1) It was found that symmetrical strain distributions in graphene result in linear decrease of the pseudogap as the strain increases. When the strain is below 30.1%, the graphene system keeps be a zero bandgap semimetal. However, as the strain further increases, the shape of the band structure changes greatly, the band crosses at the Fermi level and the DOS at the Fermi level is larger than zero, indicating that the system becomes metallic.2) Uniaxial strain distributions in graphene result in opening of band gaps at the Fermi level and the variation of band gaps exhibits an oscillatory behavior. For the graphene system with a uniaxial strain distribution along ZZ axes, its band gap firstly increases and then decrease with strain increasing. The phenomenon occurs three times until the strain up to 29.2%, and the band gap vanishes, which indicates that the system becomes metallic. When the strain is in the range of 38.9% and 68.1%, there exist a structural phase transformation in graphene, from the rhombic phase to a rectangular phase. The new phase configuration is made up of coupled linear atomic chains of carbon. As strain further increases, the distance between two carbon chains becomes larger and the interactions become weaker gradually. Consequently, the graphene system turns to be isolated vertical carbon chains.3) For the graphene system with a strain distribution along AC axes, the same oscillatory phenomenon occurs only two times and the band gap vanishes when the strain up to 26.2%. Evidently, the graphene system changes from a semimetal to a metal via a semiconductor. In the whole strain process, the system holds only the rhombic phase and finally changes to lateral atomic chains of carbon under large enough strain.4) The poisson ratio of graphene system under uniaxial strain distributions was studied. The results show that as strain approaches to infinitesimal, the poisson ratio is 0.1732, which indicates the graphene system is isotropic. As strain increases up to 1.5%, the poisson ratio of uniaxial strain along ZZ axes is slightly larger than that of uniaxial strain along AC axes, which indicates graphene system is anisotropic under large deformation.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Structural Chemistry > Chemical bond theory
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